Line interconnecting system



F. M. SLOUGH. LINE INTERCONNECTING SYSTEM APPLICA'HON FILED JAN-6,191 9.

' Patentd Nov. 28, 1922.

INVENTOR Patented Nov. 28, 1922.

"rates PATENT orFicE'.

Eaann tr. srouen, or BQCHESTER, NEW YORK, nssrenon TO THE STROMBERG- oAnLsoE rEnErHonE ,rannurnc'runrne coMrANY, or ROCHESTER, NEW YORK, a conroaarron or NEW YORK.

LINE INTERCONNECTING SYSTEM.

Application filed January 6, 1919. Serial No. 269,823.

ToaZZ whom, it may concern Be it known that I, FRANK M. SLoUcH, a citizen of the United States, residing in Rochester, in the county ofMonroe and; Stateof New York, have invented a certain new and useful Improvement in Line Interconnecting Systems, of which the following is a specification.

My invention relates to telephone exchange systems in general, but more particularly to so-called automatic telephone exchange systems in which the general operation of interconnecting calling and called lines is accomplished automatically under the control of the calling subscriber.

Generally stated the object of my invention is the provision of an improved and highly efficient telephone exchange system.

Special objects of my invention are the provision of means whereby the resulting talking connection between two subscribers may be made through a minimum of switch contacts, so that the chances for trouble due to improper connections made through such contacts may be reduced to a minimum; the provision of a novel arrangement whereby each subscriber provided with an individual line switch, may select a non-engaged trunk circuit, common to a group of such individual switches, and may thereafter by the operation of selecting apparatus, which may not be individual to such a selected trunk circuit, cause the operation of the line switch of the called subscriber to cause it to connect to the said connected trunk circuit; also the provision of means whereby after a trunk circuit has been selected by a calling line, one of a plurality of directively controlled switching mechanisms'may be selected by the calling subscriber, such a selected one being one that is not in use at the time, and the selected switching mechanism is thereaften directively operated under the control of a calling subscribers substation apparatus to locate the line switch of the called line and cause it to seek and connect to the trunk circuit first selected by the calling line.

Another object is the provision of means whereby after the interconnecting function having been performed, the directively switching mechanism may be discharged from the connection, and may be made available for the use of other calling subscribers.

To the foregoing and other useful ends, I provide certain features of construction and novel arrangements which constitute a substantial contribution to the general art of telephony, particularly the art of automatic telephony, as. will hereinafter more fully appear.

In the accompanying drawing the figure shows two telephone lines LA and LB leading to substations A and B, from individual line switching apparatus LSA and LS'B for each of the lines. Other lines and line switching apparatuses will be, of course, provided in practice, only two of them being shown for the purpose of illustrating my invention.

At TK I show a series of circuit conductors interconnecting corresponding sets of passive contacts arranged for possible engagement by the wipers of each line switch. These circuit conductors TK comprise conductors of a trunk circuit of a'group of trunk circuits, each trunk circuit of which will be similarly provided with passive contacts on each line switch of the group of line switches. Only the one trunk circuit however and the associated passive contacts for two line switches being illustrated, it being under stood, however, that other trunk circuits will be provided similar in character to the trunk circuit TK.

Associated with the trunk circuit TK. is shown controlling apparatus LK for the trunk circuit, this controlling apparatus consisting of relays,- etc., and also an individual non-numerical switching mechanism LKS with which each trunk circuit is provided. This non-numerical switching mechanism is enabled by its wipers 32, 33 and 34 to make connection with one or another of a plurality of switching mechanisms, such as the switching mechanism LSW as may be at the time in an idle or unused condition, such switching mechanism as LSW being of contacts belongin to one of adapted to be directively operated under the control of a calling substation to connect its wipers, such as the wipers 38 and 39, to circuit conductors leading to the line switch mechanism, such as LSB of the called line.

Referring now to the substation apparatus A, I show a telephone substation comprising the usual transmitter, receiver and bell illus trated by the usualsymbols and a hook switch 101, and the usual form of circuit interrupting dial DL. From this substation apparatus a telephone line LA extends by line conductors and line switch mechanism LSA. It is understood that this line and line switch are but one unitary telephone equipment individual to a particular telephone line, other like unitary equipments bcin r provided for other telephone lines, such as the equipment consisting of the substation apparatus B, line conductors LB and line switch mechanism LSB. In this description the line havin the substation A will be arbitrarily chosen as the calling telephone line, and the line having the substation B will be elected as the called telephone line.

The line switch mechanism for each of thelines is in general of a well known form, in which a set of line switch wipers, such as the wipers22, 23, 24, 25 and 26 of the line switch LSA, normally rest upon a set a plurality of selectable trunk circuits which trunk circuit was the last employed by the line switch in establishing the last established connection. Other sets of contacts for other trunk circuits lie in the path of the line switch wipers and are adapted to be successively engaged by the line switch wipers when the line switch is operated under the propelling influence of the line stepping magnet LSM.

Associated with each of the line switches are a plurality of relays consisting of a line relay L and line cut-oil relay CO, and a switching relay SWR, the first two of which control the actuation ofthe stepping magnet LSM,and control the extension of the line and local circuit controlling conductors to the line switch wipers. The relay SW'R is adapted to be operated when the line with which the line switch is associated is a called line, and in which case it switches certain connections as will be later described, in order to make the line switch mechanism perform its trunk hunting operation under a different kind of control from that exercised by it when the line with which it is associated is a calling line.

Associated with each line switch, such as the line switch LSA, are a plurality of sets of passive contacts, one set being provided for each trunk circuit with which connec tion may be made by the line switch. Two of these sets of contacts are illustrated in the drawing one for each of the illustrated line switches, but one of them however, thatone consisting of contacts 27, 28, 29, 30 and 31 for the line switch LSA being shown as connected to the circuit conductors, as TK, of a trunk circuit; it will be understood though that each set of contacts with which the line switch is provided, of which there may be 10 or more sets, will be likewise connected to a similar set of circuit conductors, through which circuit conductors telephonic interconnecting and switch controlling circuits may be associated between calling and called lines through the intermediary control of trunk controlling mechanism, such as LK of the trunk circuit TK.

With the switching relay SWR of a given line switch, such as the line switch LSA in its normal or unoperated position, which is the position which is assumed when the associated line is a calling line, throughout the ensuing connection, only the line switch wipers 22, 23 and 26 are connected to the circuits of the line switch, the other wipers 24 and 25 being operatively disconnected therefrom, and during such a connection are unused. It is only when the line is a called line and the relay SVJR of the called line switch is operated, that these wipers are used and are operatively connected to the line switch circuits to perform functions in connection therewith later to be described. In passing it may be said that such line switch wipers corresponding to the wipers 24 and 25 of the line switch LSA for the line switch LSB, are shown at l and 5.

hen a call is initiated over a calling line, such as the line LA, a connection is thereafter automatically made to an idle trunk circuit, such as the trunk circuit TX by means of the line switch, such as LSA, cer-- tain apparatus LK of the selected trunk circuit TK, is thereupon placed under the control of the calling subscriber, and under this control an individual switch mechanism LKS for the selected trunk circui TK, is thereupon operated to extend controlling c' "cuit conductors of the trunk circuit TK to circuit conductors of an idle or unused numerical switch mechanism diagrammatically illustrated at LSXV. This numerical switch mechanism may be of any of the well known forms, but in this description it will be, for convenience, considered to be of the form well known in this art, which consists i of a switch brush carriage adapted under the successive control of successive series of impulses to cause switch wipers attached to this carriage to be conveyed first, under the control of the first series of impulses in a vertical direction to select a group of contactsets, and then to be conveyed in a horizontal direction to select of the group a contact set which is connected to circuit conductors leading to the called line apparatus. lln the thismaking for simplicity of design of the switching mechanism.

Associated with the switch mechanism LS W, I preferably provide the usual forms of controlling means, consisting of a primary stepping magnet PM for propelling the wipers, for instance, in a vertical direction, and a secondary stepping magnet SM I subsidiary slow releasing relay RR, other subsidiary slow releasing relays D and KL- and relays Y, Z, and X are provided for purposes hereinafter set forth. Common control means for a plurality of such switching mechanisms, as the mechanism LSVV are provided consisting of the restoring switch RSVV adapted to contact with passive contacts, such as the passive contact102 associated with the switching mechanism LSVV, for each of the associated switching mech anisms of the group and astepping magnet F for the said restoring switch, together with a relay E, controlling the same. This common controlling means is provided for the purpose of preventing more than one called line switch selected by the numerical switchin mechanism LSW from operating at a time, so that on simultaneous calls be-' ing made to a plurality of such numerical switching mechanisms, within an interval following such a call, only one called line switch may, as such, operate at a time insuring that connection will be made to the proper line desired.

Having now described the instrumentalities employed in the illustrated embodiment of my invention, 1 will now describe the operation of the same in detail, reference 1 being made to the drawing in which as above stated, election is made of the line having the substation A as the calling line, and the line having substation B as the called line.

Assume that the subscriber A initiates the call by taking his receiver fronrthe hook and closing the hoolr switch contacts 101, a circuit being therefore closed through normal contacts 102 and 103 of the cut of? relay CO, to slow releasing line relay L, the common source of current BTY being included in this circuit to cause the operation of the line relay L, which being operated will attract its armatures closing contacts,

104; and 105, the adjustment of these contacts being preferably such that the contact 104 will be definitely closed prior to the closure of the contact 105. At this time the line switch wipers 22, 23, 24-, 25 and 26 had been resting upon a set of trunk circuit contacts as illustrated, and it is to be assumed in this description that this set of contacts is connected to circuit conductors leading to a busy or used interconnecting trunk line, and that therefore because of the busy condition of such a trunk line, the contact upon which the wiper 26 at the time rests, is connected to the ground pole of the common source of current BTY, and that therefore a circuit is closed including the winding of the stepping magnet LSM of the line switch including the common source of current, this circuit being traced as follow: from the ground pole of battery, through the common source of current, tne winding of the steppingmagnet LSM, normally closed contacts 106 carried by its armature, now closed contacts 104; of the line relay L, normally closed contacts 107 of the relay CO, normally closed contacts 108 of the switching relay SWR, and from thence through the wiper 26 to ground, which we have described as connected to the passive contact upon which this wiper 26 rests. This circuit beclosed, the stepping magnet LSM will be thereupon actuated, and because of the contacts 106 carried by its armature being thereupon broken, will again immediately retract'its armature, the mechanical connec tion between the armature and the wiper carrying member being preferably such that the same is advanced upon the retraction of the armature, he arrangement in this respect being like that illustrated in the appli cation of Bert G, Dunham, S. No. 227,462, filed Got. 6, 1904s. Therefor, the switch wipers of the line switch'will be advanced from the passive set of contacts upon which theyhave been resting, to the next succeeding set of passive contacts consisting of the contacts 27, 28, 29, 30 and 31 associated with the trunk circuit TK. The wiper 26 will be so constructed that at no time will it pass out of contact with all of the contacts in its path, that is, it will be provided with a broad enough wiping surface so that in contacts, it will make contact with the second contact prior to the breaking of the contact with the first contact; thus as long-as the wiper 26 engages both trunk lines whose contacts adapted to be engaged by the wiper 26 are therefore connected to ground, the circuit for the stepping magnet LSM' will be continuous, and thestepping will continue until such condition is over by the final car- Tying of the wiper 20 into contact with a passive contact such as the passive con- 31 engaged tact 31 of the trunk circuit TK, which contact is not connected to ground, signit'ying that the associated trunk circuit is in an idle or unused condition. Under ':h a condition, the low resistance connectron to ground which has prevoiusly been existing through the contact wiper 26, is removed and a hi gh resistance connection only to ground remains, this comprising the wind ing oi the cut oil relay C0 and now closed contacts 105 of the line relay L. The winding CO being traversed by ourrei t on account of its inclusion in the enerusing circuit of the steppinginagnet LSM, which circuit includes the source BTY will attract its arz'natures. In the meantime, however, the stepping magnet LSM will cease the intermittent operation of its armature, since the resistance of the winding C'O is too high topermit enough current to pass through it to operate the magnet liSitL'.

The armatures of @O being attracted, the

line r lay magnet L will have its circuit opened at the contacts 103 which are now broken, and will being slow releasing slowly restore its contacts d and 105 to their normal open condition.

During the period of deenergization of the line relay L, the lower armature of the relay U0 passed from its normal position wherein it maintained the contacts 107 closed, to its operated position, wherein contacts 107 are opened and its front contacts are closed, the energizing circuit maintaining the relay CO operative after the line relay releases its armatures being traced as follows: from the ground pole of the source BTY, the said source, the winding of the stepping magnet LSlvl, normal contacts 106 thereof, the winding of the relay CO, now closed contacts 109 thereof, normal contacts 108 of the relay Sll li, switch wiper 26 and passive contact thereby, and now closed contacts 110 of slow releasing relay LSR associated with the trunk circuit, this relay having been previously operated prior to the release by the line relay L of its armatures,

The circuits involved in the operation of the relay LSR will now be traced: when the line itch wipers22, 23, 2a, and 26 made connection with the set of contacts 27, 28, 29, and 31 of the trunk circuit TK, and after the relay CO was operated as above described, the line conductors LA or" the line having the substation A would extend through now closed contacts 111 and 112 to switch wipers 22 and 23, and by interconnection of these wipers with the passive contacts 2i" and 28 of the selected trunk line, the line conductors would extend to the trunk controlling apparatus LK, where a bridge of these conductors consisting of the impedance coil ZZ and the relay SR, together with the included common source of current BTY was made.

which busy tone generator thereupon begins,

to project busy tone current over the calling line conductors, the circuit for the projection of the same leading to the passive contact 2'7, through normal contacts 115 off a tandem wound slow releasing relay BL, the now closed contacts 11-1 of the relay LS3, and normal contacts 116 of the relay 117. This busy tone current will persist until after the dialing operation by the subscriber has been completed, and will be discontinued in that case only if the called for line is found to be idle, or under such other conditions as will later appear.

Gther means of controlling the busy tone circuit might be provided in place of that herein specifically set "forth, the particular method of control therefore which is herein illustrated and described, being chosen because of its simplicity and lack of complications insuring positive and unyarying operations of like nature under similar conditions.

Upon the relay SRbeing energized, a circuit is likewise closed for the individual vitch line relay LMR of the individual switch which is associated with the trunk circuit TK selected, this circuit being traced from the ground pole of battery, through contacts 113 of the relay SR, normal contacts 118 of the relay BL, normal contacts 119 of the individual switch cut-off relay COM, the winding of the line relay LMR, which is made slow releasing in a like manner and for a similar purpose as was done in the case of the line relay L for the line switch LSA, the circuit being continued to the common source of current BTY to the ground pole of battery thereof. The closure of this circuit at the contacts 113 will cause the energization of the relay LMR and which retracting its armatures, will close successively the contacts 120 and 121, the successive closure being secured by proper adjustments'to cause the individual switch mechanism to operate. to make connection with an idle or unused numerical switch mechanism, such as the numerical switch mechanism LSl/V whose incoming conductors NSC terminate in passive contact sets, such as the contact set comprising contacts 122,35, 36 and 37, in each individual switch for each trunk circuit of the group of trunk circuits employed. The individual switch mechanism LKS, except for the absence of the switching relay SVVB is structurally very much like the line switch mechanism LSA, individual to the different lines, certain differences being of course required by ditlerent conditions under which the individual switch mechanism LT'IS must operate.

The active switch wipers 123, 32, 33 and 34 normally rest upon the passive contacts which although, not so shown, would be connected by conductors like the conducto NSC to the numerical switching mechanism of the same group as, and like unto the numerical switching mechanism LSVV. Should such a numerical switching mechanism be at the time engaged, the passive contact upon which the wiper 3s normally rests will be connected to ground in a manner which will be made more apparent in the description which follows for the switching mechanism LSYW.

Suliicient for the present, however, is it to say that the presence of this ground denotes a busy switching mechanism and causes the non-numerical switch LKEB to advance its wipers into engagement with the next set of contacts, and this action may be repeated if the next set or" contacts is associated with a busy numerical switching mechanism until a set of idle contacts, such as the set comprising the contacts 122, 35, 36 and is reached, whereupon there will be found no ground connection to the contac 37 at the time engaged by the switch wiper 34;, and that therefore the current through the stepping magnet MSM for the switch LES will be cut oil, and the cut-off relay COM will be energized in exactly the same way as was the case as before described for the switch LSA, reference in that case h. ing in this description been made to the similar and the similar cut-oft relay CO, so that for brevity this operation will not be re-described in detail.

Sutj cient to say at this time, that when the contacts of an idle switch mechanism as LSlV are reached, the wipers will be stopped in engagement with these contacts, the cut-off relay COM energized being held energized over a circuit comprising in part the wiper 34, passive contact 37, the normally open or now closed contacts 1240f the slow releasing relay RE which for this function corresponds to the slow releasing relay LSR, which relay RE is held operated by normally open but now closed contacts 125 of a relay 1B which corresponds, for this function, to the relay SR, the operation of the relays LSR and SE in corn nection with the switch LSA having previously been described. The relay TR now operates over a circuit including the active switch wiper 33 and the passive contact 36 of the switch IKS, and through normally vupon "functioning stepping magnet LSM' open but now closed'contacts 113 of the relay SR; so that it is under the control of the relay SR, being operated when the rela'ySlit is operated and released when the relay SR maybe released. The relay SR being at all times under the control of the subscriber at the calling substation A, the relay IR is likewise under this control, the action 01" the subscribers dial DL and switchhook contacts 101 upon the relay SR being'repeated by the relay SE in its control over the relay TR during the period through which the switching mechanism LSV, with which the relay IR is associated, remains in association with this connection. The relays IR and RR are a pair of fast and slow relays which operate in a well known manner under the control of the calling subscribers dial, as DL, to cause the successive operation 01": primary and secondary stepping magnets for the switching xnecQanism LSW. This operation will now be described.

The subscriber first operates his dial to interrupt the circuit of the relay TR a certain number of times, and IR will thereretract its armature a certain number oi times, dependingupon the first digit of the called line number.

The contacts 125 will thereupon be opened 9 for very short periods during these interruptions, but such openings as will thereby be introduced in the. circuit of the slow releasing relay RR, will not cause the relay HP.- to retract its armatures. Consequently upon each closure of the normal cont-acts 126, a circuit will be completed for the primary stepping magnet PM, this circuit including the slow releasing rela D, which will keep its armature attracted during the series oi circuit interruptions, and for a brief period thereafter for a purpose which will, be described, but which will be well understood by those versed in this art when it is explained that the relay 1) controls the escape magnet Y for the side switch havmg wipers at, 45, 46 and 47, and that this escape magnet Y advances these side switch wipers upon each deenergization. During the first series of circuit interruptions, the side switch wipers are in first position, as shown. The primary stepping magnet PM having its circuit closed at the contacts 126 a definite number of times, will step the switch carriage carrying the wipers 38 and 39 in a primary direction a corresponding number of steps to locate the group in which the passive contacts 4:0 and er of the called line are located.

In passing it will be understood thatthe passive contacts for each line are multiply connected in the different numerical switching mechanisms of the system, of which the switch mechanism LSVV is one. This 1s also true of the passive contacts, such as 122, 35,

36 and 37 which are multiply connected to other like passive contact sets for the other individual switches TKS of the other trunk circuits of the system, this in a manner like that illustrated for the trunk circuit TK, which has, as illustrated, multiply connected passive contact sets for the telephone line switches, such as the line switch LSA and the line switch LSB. This system of multiply connected contact sets for different switches is well known in the art and will not therefore be described in all its aspects. At the end of the first series of circuit interruptions, the contacts 126 being there upon opened for a definite, relatively long interval, current in the circuit of the slow releasing relay D being thereby interrupted for a sutficient interval to allow it to retract its armature; and the slow releasing relay KL which has been held operated by the closure of the contacts 48 of the slow releasing relay D, will soon after retract its armature, opening the contacts 49 in the circuit of the escape magnet Y, which magnet has been kept energized by the closure of these contacts 49; and the escape magnet Y now being deenergized by the opening of these contacts, the side switch wipers 44, 45, 46 and 47 will advance to their second operative position. In the second position various circuit changes are effected as will now be described.

Previously, however, certain sets of contacts known as ofi normal contacts and illustrated in the drawings at various places and marked with the reference characters ON, have been operated, this operation being accomplished in the well known manner upon the first movement of the switch carriage under the control of the first impulse of the first series of circuit interruptions. The efiect of the operation or" one of these ON contact sets is to close the contacts O insuring that a connection to ground is maintained on the passive contact 3'? of the switch LKS, to maintain the cut-cit relay thereof, COM, operated until the final later restoration of the switch LSlV to normal, whereupon these contacts 50 will be opened as will be later noted.

The subscriber will now again operate his dial to produce a second series, containing a certain definite number of circuit interruptions to step the numerical switch wipers 3S and 39 in a secondary direction to locate the terminals 40 and 41 associated with the called line desired. This stepping is accomplished by the intermittent operation of the contacts 126 in the circuit of the secondary stepping magnet SM, which circuit as in the case of the stepping magnet PM contains the slow releasing relay D which relay is maintained energized during this second series of circuit interruptions and caused to release its armature shortly after 1 name? the circuit interruptions have ceased. The circuit above mentioned is traced as follows: from the ground pole ot. battery, through the contacts 126 of the relay TR, through the now closed contacts 51 of the slow releasing relay Hit, the winding of the slow releasing relay D, normal contacts of the relay X, normal contacts 53 of the busy test relay ET, the winding ot the secondary stepping magnet SM, second position passive contacts and side switch wiper to the negative pole of the source of current and through the said source BTY, to the ground pole of battery. Current from the said source besides keeping the slow rcleasing relays U and the controlled slow releasing relay KL continuously opera-ted, will cause the escape magnet Y controlled by the relay KL to be energized by the closure of the contacts 49 of the relay KL, and will also intermittently operate the secondary stepping magnet SM a definite predetermined number of times according to the number of circuit interruptions oi the second series to cause the stepping of the switch wipers 38 and 39 to contact with the passive contacts 40 and 4.1 of the called line.

The relay X will not be operated at this time regardless of the condition of operation. of the re ay Z, which for the present we will assume is in normal un-operatcd condition, since the closure of the contacts 54 ot the escape magnet Y and the circuit thereby extending through the second position passive contacts and side switch wiper 47 through the winding of the relay X, and from thence to normal contacts 55 of the relay Z to ground, will be shunted by the prevailing direct connection to ground through the con" .c'i's 49 oi the relay KL. However, at the end of this second series oi impulses and the contacts 1P6 being definitely opened it. a given length of time, the relay D will retire its armature, opening the contacts 48 in the circuit of the slow releasing relay KL, which, retiring its armature, will open the direct connection to ground through the contacts 49, removing the shunt hitherto established about the winding oi" the relay X; and the relay X, assuming the continued non-operational the relay Z, will be operated in series with the winding of the escape magnet Y, preventing the de-energization of the escape magnet Y for the time being, or until the circuit in which the winding of the escape magnet Y and the windof the relay X is later opened upon the subsequent operation or'f the relay Z. The relay X being operated completes a circuit for the relay 117 controlling the busy test circuit, by the closure of the contacts 100 of i the relay X; this causes the relay 117 to be switch LKS, the said contacts 100 and the source of current BTY which energizes the relay 117, causing it to open contacts 116 in the circuit of the busy tone currentsource BZ, so that during the period prior to the control. of the called line switch by the switching mechanism LSVV, the busy tone current will not be projected to the calling subscriber, if the called line is not busy.

Now the switch having the wiper RSW is shown as a rotary switch with wiper traversing, illustrated, live passive contacts in successiolnit being taken for granted for the purpose of description that the rotation is in a clock-wise direction. Each of these passive contacts, such as the passive contact 102 is associated with a dili erent numerical switching mechanism, such as the switching mechanism LSVJ tor the contact 102, and whenever the side switch wiper RSW is at rest upon one of these contacts, the associated numerical switching mechanism may exercise a control over one of the line switches o" the system, which line switch is one belonging to the line called by the calling subscriber who at the time has control over the particular associated numerical switching mechanism. Thus only one of the switching me hanisms oi the group containing the switching mechanism LS i may operate a called line individual switch at the same time. This is to prevent wrong connectionsbeing secured by calling subscribers, and other difiiculties which might ensue were this not the case.

If the switching mechanism RSVV doesnot rest upon the contact 102 of the switching mechanism LSlV, when as in this description the time has come for the switching mechanism LSVV to exercise its control over the called line switch, then, it another switching mechanism is not at the time eX- ercising such control, by the operation of the relay X as previously describes, the switching mechanism LEFW may cause the wiper llSlV to advance step by step under the propelling influence of the stepping magnet 11 to the position wherein it contacts with the contact point 102 of the numerical switching mechanism LSl V, whereupon the stepebystep motion will cease. The stepping magnet F under such a condition is actuated over a circuit traced as. follows: from the ground pole of battery, through normal contacts 56 of the relay Z, the normally open or now closed contacts 57 of the relay X, the normal contacts 58 of the common controlling cut-oil relay E, and from thence through normal contacts 59 mounted on the armature of the stepping magnet F, throughthe winding of the said stepping magnet, through the source of current BTY, to the ground pole of battery. The stepping magnet thus will be intermittently operated under the controlling influence of its intermittently broken contacts 59, until the wiper RS1? coming into contact with the contact 102, will close a circuit for the relay Z, in which circuit the common controlling cut-oil relay l) is also included to operate the relays Z and E the circuit being traced as follows: from the ground pole of battery, through now closed @h contacts, the winding of the relay passive contacts 102 and switch wiper RSlV, the winding of the relay E, through the source of current BTY to the ground pole of battery.

The relay E having operated, will break the circuit of the stepping magnet at 58,

which circuit will also be interrupted by the operation of the relay Z the contacts The contacts 55 of the relay Z also being broken, will interrupt the circuit of the relay X, and the escape magnet Y will,

also be restored to normal, the escape magnet 1 allowing the side switch wipers to pass into third position. This is the position in which the called l ne switch is operated under the control of the numerical switch Lil i i and in describing the operation of the system up tothis point, it has been assumed that the called line was in a tree or idle condition, and that therefore connection might be made with the same by the calling line. However, if this was not thecase, the side switch wipers would be prevented from advancing into third position, as will now be described.

Under; the assumption that the icalled line was busy at the time that the side switch wipers were in second position and after the end of the second series of circuit interruptions to select the called line, a circuit would have been closed for the busy test relay Bil and the slow releasing relay KL, as soon as the slow releasing relay D had retracted its armature again restoring its normal contacts 60. This circuit may be traced as follows: from the ground pole of battery, through the source BT1 the winding of the slow releasing relay KL, the normal contacts 60 of the slow releasing relay 1), the winding of the busy test relay Bil, normal contacts 61 of its set of make before break contacts, second position contacts and side switch wiper e5, numerical switch wiper 39, the passive contact 41 of the called line, and from thence to ground which will be placed upon the conductor leading to the contact 4L1 whenever the cut-ofi relay C0 of the called line is energized, as has been de scribed, and line relay L is energized, ground in this case being placed on the conductor leading to the contact ll from the normally open contacts 62 or the line relay L. Therefore, on busy line condition current flowing over this circuit would ener ize the busy testrelay Bil, and the slow releasing relay KL and these relays would attract their armatures, the armature for the relay BT closing lockingcontacts 63, and causing the subsequent opening of the contacts 61, the latter to open the testcircuit leading to the brush 39. The locking contact 63 being closed. a locking circuit for the relays HT and KL will be completed therethrouggh, traced follows: from the ground pole of battery, through the now closed off normal contacts UN, through the contacts and the winding of the relay RT, through normal contacts 60 of the relay D, through the winding of the slow rerelay Ill through the source of curren BTY to ground.

The contacts l9 of the relay KL being closed, will maintain the escape magnet Y energised and the off normal contacts ON will maintain this condition continuous until the restoral of the switching mechanism LSl V to normal. In the meantime the subscriber having'completed the dialing operation, will place the receiver on his ear, and the line being; husy nothing will occur to remove the busytone current from the busy tone source 1325 fromthe line the application ofsuch source having as described previously occurred, the characteristic busy tone sound will be heard in the receiver and the subscriber will know that the called line is busy, therefore not accessible for a connection and will therefore retire his substation instrument, opening the contacts 101 of his switchhooh at the substation A.

The opening of the switchhool: 101 will automatically restore the central oiiice mechanism to normal. First the relay SR in the substation line circuit will be r storeiil. opening the contacts 113 in the circuit of the relay LSR of the trunk circuit controlling apps atus LK retiring this relayand in the c "cuit of the impulse relay ll? of the switching mechanism LSW', which relay will also be retired. The relay Ti l being" retired, will retire the relay and a circuit will be completed for the release magnet of the switching mechanism LEYW including normal contacts 126 of the relay Ill, normal contacts Gt of the relay RR, on? normal contacts ON and winding of release magnet RM, through the source of current BTY to ground. Current from the said source will energize the release magnet to restore the switching mechanism LSN, a

locking circuit for the release magnet being closed through contacts 65 and the off normal contacts ON to insure that the release function will continue until the switch is entirely restored to normal. After this has occurred, the ground at the off normal contacts 50 and the normally opened contacts 124- of the relay RR being removed from the conductor leading to the passive contact 37 of the individual trunk switch LKS, the trunk switch LKS will be restored to normal by the subsequent retiring of the out 0E relay COM opening all of its contacts. The wipers of the trunk switch will remain qui escen t as the individual switch illustrated and described is of that type wherein the wipers do not return to any special position after each connection, being); merely operatively dissociated from the controlling circuits by the opening of relay contacts at the end of the connection. Such a switch is shown in the application of C. C. Bradbury, Serial No. 556M 66, filed ltlay 16, 1910, reference to which may be had for the purpose of securing a better understanding of such a switch than this brief description thereof aii'ords.

The relay LSR of the trunk controlling apparatus Ll: having been retired as previously described, the ground connection to the passive contacts 31 of the calling line switch LSA will be removed by the opening of the relay contacts 110 of the relay LSR, thus restoring the cut-off relay C0 of the line switch LSA, which restores the apparatus of this line switch mechanism to its normal. position. All of the apparatus involved in theattempt to make connection with the called line has now been restored to normal.

To resume the narrative ofthe connection, at the point where the same was broken OH, to describe the operation of the circuits in case the line was found to be busy, we will now continue the narrative making the assumption that the line called for was not busy but idle, and therefore available for a connection. The narrative is resumed at that point wherein the side switch. wipers 14.. 4-5, 4-6 and t? had advanced into third position.

Side switch wiper 46 being in third position will connect battery in the circuit of the relay CT. through passive contact 35 and active wiper of the individual switch LlCS, normally open contacts 66 of the relay COM, winding of relay CR, through normally made contacts 118 of the relay Eli and normally open contacts 113 of the subscriber controlled relay SR. The slow releasing relay CR will thereupon be ener- 'ized, one effect of the energization being as follows; the normally open contacts 67 will be closed completing a. circuit including battery the resistance coil 68 for the relay BA the normally open contacts of the relay SR which being energized will attract its armatures. The closure of the contacts 69 thereby completes a locking, circuit for the relay RA likewise including battery, the resistance coil 68 and the normally open contacts 70 of the subscriber control relay SR. The relay EA will therefore for the present be held actuated by virtue of this locking circuit. i

The relay CR being operated will also open the contacts 71 and close the contacts 72, first removing-thenorrnal direct ground connection to the test conductor78 of the trunlcc'ircuit TK' and the second substituting therefore a relatively highfresist'ance ground connection including the winding, of the relay" RL; Thus instead of a 'direct ground bemg'placed upon the passivecon ta-cts 10 associated with the trunk TK on the i contacts "116 of relay 'l17,- normally *openf contactslll of, the relay LSR-jand normal contacts 115" of the 'relayjRL tothe trunk line tall ringconductor leading tothe passive contact of the 'callingfline'switch' and from thence to the calling -linei zwill have been interrupted by the opening of the contacts 115 whzhthdrelajr 'RL was operated;

which"a's has been described, occurred immediately following the] movement of the side switclr'wipers into thirdposition.

The side'switch wiper 44 passing into third"positiomiwill extend a direct ground connection to a terminal of the relay SVVR of the called line switch LSB, through active switch'wiper 38 of switching mechanism LSWVand'passive contact 40' of the calledv line locatedtherein, this circuit being traced throughthe w-indingofthe relay SWVRincludes the sourcejof current 'BTYand being closed, causesthe energization of the relay STVR," "which being energized attrac'ts its armat-ures switching circuit asfollows First the lower armature beingattracted:breaks the contact 74 in the circuit offthe activeswitch wiper 6 whiclrwh'en the line with' whichit isas'sociated is acalling, line,lis

known as the test "wiper, and the closure of the' contacts 75 substitutes [the active switch wiper 5 as the test wiper in place ofthejtestfwiper'fi thetest wiper 5 beingin operation when the line is a called line, and thetest WiperG'beingin operationrwhen the lineiis a calling line. Likewise the line wiper4, when the'contacts 76 are cl'osedzuidthe contactsl'f are opened,"1s substituted;

for theline wiper'3, the l'in'e wiper being, used when 'the line is a*called line and the line wiper 3 being usedwhen theline is a calling'line. i

' Tlie'contacts 78 being closed will complete a circuit for'theline relay L, this circuit being traced, from ground through the con tacts 78, now clo'sed,'tl1e normal contacts 79 of the relay C0,;throughthe' winding of the slow releas'ing'line relayL zand the line relay-L being caused to operateywill close its contacts 180 and 62 successively,

just as did the line relay-L oi the'line LA close its contacts 10a and 105; as has been previously described when the line LA was I source of current BTY to ground. I The 7 I initiating the call. "The closure of'the con t acts -180 will complete a circuitfor the stepas follows: from the ground pole of battery ping magnet LSM, the circuit being traced 4 75 the windingofthe stepping magnet 'LSM',

normal contacts 81 thereof, the now closed "contacts of the relay L, normal; contacts 82 of the relay COynow closed contacts 75 ofthe relay SVVlit, called line test Wiper 5,

and from thence to whichever of the passive" contacts corresponding'to the passive con- 'tacts 10 of the'trunk circuit TK, as may be" m contact with the test wiper 5 atthe -inoment this circuit is closed, the circuit being-"85 continued from suchan assumed test con} [tact lOfof an assumed other trunk'circuit corres'p'ondlngin structure to the trunk c1rcuit TK, with whlchthe assumed passive contact lO is associated, through normal contacts 71 lot-a relay such as OR, to ground, I All trunk circuits except thetrunk circuit TK will maintain through su'c'hcontacts; as

the contacts 71, a normalground connection' to its passive'contacts 10, so that'the circuit for the stepping'magnet LSM will be com- "pleted to ground wheneverand during the time thatthe wiper 5 rests uponone of such other test contacts. pingmagnet LSM, intermittently operated This causes'the step- I under-the control of its own norrnalconr tacts 81, to step its associated set of wipersj 2, 8, 4:, 5 and 6 from trunk circuit to trunk circuit passive contact-s until the wiper '5 I comesfinto contact with the test contact 10- of the-trunk circuit TK used in building up this passive contact 10, but only a connection through a resistance coll conslstmg of a winding of the relay RLpQSufiiciehtcurrent will not flow over this/circuit through the said winding and through the winding this connection, and when this occurs there I being no direct connection-from ground'to of the stepping magnet LSM' to operatively energize it, consequently the stepping magnet will'cease the stepplng'of the wip-ers'and will remain qulescent with its associated wipers resting] in contact with the set of contactsin which is contained the'contact 10, which set is that'one-associated with the The relay. RL will be trunk circuit TK. operated and operatively locked, the locking circuit including the source of current BTY, the winding '83,"now closed normally open contact 84- of the relayRLpand nor-" mally open contacts 113 of the relay SR,

now closed. The relay C0 of the line switch LSB,- will at the's ame time be operated just as was'the line switch relay" C0 of the switch LSA,Wl11Gl1 operation has been described, and which will not now be repeated.

In like manner the slow releasing relay L will be retiredas was the case with the corresponding relay of the calling line circuit, and the line conductors LB will be extended by the closure of contacts 85 and 86 of the relay CO to the line switch wipers 2 and 4E, and. thence through the passive contacts 7 and 9 of the trunk circuit TR, to the line conductors 87 and S8 of the interlinking colrtrolling circuit LK of the trunk circuit T The contact 79 of the relay CO will be broken, opening the circuit of the line relay Land the contacts 89 will be closed, maintaining the relay SYVR in operation independent of the connection through the side switch wiper 44; and third position contact therefor.

The relay RL being operated will cause the release of the individual switch LKS of switching mechanism LSW all of which will now be restored to normal. This is primarily caused by the opening of the contacts 118 in the circuit of the relays IR and GB. The relay IR is therefore deenergized retiring its armature likewise causing the retiring ofthe relay BR, and a circuit for the releasing magnet which has been previously described, is completed through normal contacts 126 and 64 of the relays IR and RR respectively. The said release mag- 7 net RM being energized, causes the switching mechanism LSW to be restored to its normal position of rest, and the above having occurred, ground connection will be re moved from the passive contact 37 of the individual switch LKS, which ground con nection through contacts 90 has hitherto maintained the cut-off relay COM operative which will now retire its armatures, thus restoring the circuits of the individual switch LKS to normal.

, The relay RL being operated, also opens its contacts 152 and closes contacts 153. This is accomplished prior to the opening of the contact 72, subsequent to the opening of the circuit of the relay CB, which is slow releasing, so that there will be no actual rupture, and the circuit of the circuit conductor 155 will subsequently be maintained continuous through now closed contacts 153 of the relay RL, now closed contacts 154: of the relay SR, to the ground pole of battery, thus. replacing the resistance connection to ground, through the winding of BL with a direct connection to ground, through contacts of relays mentioned RL and SB; this toisolate the trunk circuit TK to subsequently operating called line switches involved in other connections. At this time the relays SR, RA, LSR and RL in the controlling circuits LK of the trunk circuit TK are all operated, and in consequence a circuit is completed for the 4 in connection therewith, now closed contact 76 of the switching relay SWR, now closed contact 86 of the relay CO, one of the line conductors of the line LB, through the signal bell Z), associated condenser and normal switchhook contacts and dial contacts of the substation B, the other line conductor, now closed contact 85 of the relay 00, active switch wiper 2 andpassive switch contact 7, line conductor 87 of the trunk circuit TK, and from thence through the resistance coil 94L and now closed contacts 95 of the relay BA to ground. The interrupter I alternately includes the generator G, or the resistance coil 96 in this circuit to produce ringing or silent periods. I

The subscriber at the station B responding to the ringing of his bell, will remove his receiver from the hook completing an operative circuit for the flow of direct current from the source BTY, current from which source will be superposed upon the ringing current duringthe ringing period, and will cause the operation of the ringing trip relay TR, which is so adjusted and constructed to be only operative to the flow of direct current to continuously close its contacts 97. These contacts being closed, will short circuit the winding of the relay RA to deenergize the same and to cause it to retire its armatures, thus breaking this locking circuit hitherto existing through its contact 69, as described. The relay CR- having been retired when the switching mechanism LSlV was retired, the contact 69 being once opened, as described, the relay RA cannot again be operated during this established talking connection.

The talking connection is now established by the release of the relay RA, by the closure of contacts 98, which contacts being closed interconnect corresponding line conductors of each of the connected lines through a condenser KK, a connection for the flow of battery current existing for each of the lines and connected to each side of this condenser, connection for the calling line existing through the winding of the calling subscriber controlled relay SR, and for the called subscriber through the impedance coil 99. A common connection In the ground pole of battery for both of the lines exists through the impedance coil ZZ.

For the sake of added clearness it will be 1 ,as'a'ser explained I that now the flow of talking currents will be had over a circuit extending from the substation A including the line conductors LA, now closed contacts 111 and 112 of the calling line relay CO, active Wipers 22 and 2301? the calling line switch LSA, passive contacts 27 and '28" of the trunk'circuit 'TK, and from thence to'the line conductors LB or" the called line through a passivec-ontact 7 and active wiper 2 of the line switch LSB and now closed contacts-85 to one line conductor, and through the condenser KK and normal'contacts 98 of therelay RAQpassivecontact 9 and active wiper-4L of the called line switch LSB now closed contacts 76 of the relay SWR, and now'closed contacts 86 of the relay CO ito the other line conductor of the called The subscribers now being in conversational circuit will be able to converse, talking batterybeing supplied for the transmitters until-such timeas the conversational period is ended, whereupon the calling subscriber A will retire hisinstrument, thus opening the switch contacts 101 in the circuit of the subscriber controlled relay SR, which opening the contacts 113 in the operating cir cuits of'the relays LSR and BL will restore these'relays, the relay CR having already been restored, as described The relay LS R being operated Wlll open the groundcon nection' to thepassive test contacts of the trunk TK hitherto existing through the co'ntactllO, and the cut-off relay CO in the circuit of these contacts will be restored to normal; Also the relay SR deenergizing will cause its contacts 15am be opened for definite interval preceding the subsequent closure of the contacts 152,so that for a moment the circuit conductor 155 will be interrupted, it being understood that the relay BL is relatively slow releasing, and during this interval the rela C0 of the called line switch will be released, its winding being previously energized over a circuit including the conductor 155. Subse-- quent tothe release of therelay G0 which restores the circuits of the called line switch LSB to normal, contacts 152 will again be closed replacing a lcon'nection 'to ground upontheconductor 155 and the passive contacts associated therewith in the different line switches through normal contacts 71 of anisms' adapted to be directively controlled,

the relay CR. I

The circuits have now all been restored to normal and may be used again in establish-v description of preventing the rotation oi. the

switchwiper RS11 when one of the switching mechanisms, LSlV'isexercism-g a control switches for the use of each of the said lines, a group of trunk circuit-s common to the I 'saiditrunlc lines, a plurality of directively controlled switching mechanisms, a non-nuover a called line switch, this time interrupting the circuit at its opened contacts 58 of the stepping magnet F of the rotary switch having the wiper RSVV. This for a. purpose made plain from the description. I

7 It will be understood that while I have I do not desire to be limited to the specific structures illustrated and described, but am aware that numerous and extensivedepar tures may be made without departing from I the spirit of the invention.

What I claim'is:

1. In a telephone system, the combination with a calling subscribers line, a called subscribers line, non-numerical trunk finding said lines, substation apparatus for the said lines, means responsive to calling line sub-' station control to operate the calling line switch to make connection with one'ofthe merical switch for each of the said trunk circuits, means associated therewith tocause the said trunk circuit non-numerical switch with whichthe said calling line is associated to operate to connect to oneof the said switching mechanisms, means responsive'to calling line substation'control to operate the said switching mechanism to make conneetion with a terminal associated witha desaid connection to cause the said non-numerlcal trunk finding switch of the called line to operate to connect the called line with the said trunk circuit to which the callingv line has been connected, and ineansrespon sive to the connection between the said trunk I stations for the said lines, a main station, a

singleindivi'dual line switch for each of the lines at the main station, a plurality of trunk circuit and the said called line to dissociate circuits, means associated with each of the individual line switches to cause the same to connect 1ts line with an idle one of the said trunk circuits, a plurality of switching mechnon-nurherical interconnecting means to interconnect an idle one of the said switching mechanisms and a trunk circuit to which connectionhas been made by a calling line, by the'operation of the calling line indi 'vidual switch, a sending mechanism at the said substation adapted to control the d1rective operation of the said switching mechanism to cause-it to make connection'witha terminal of a desired called line, means 100 sired called line, means responsiveto the responsive to the said connection to cause the called line switch to make connection with the same trunk circuit previously connected to by the calling line, and means responsive to this last caused connection to dissociate the said switching mechanism.

3. In a telephone system, the combination with a plurality of telephone lines, substations for the said lines, a main station, an individual switch for each of the said lines at the said main station, plurality of switch wipers for each oi the said line switches, a plurality of trunk circuits in a group common to the said lines, terminating contact sets for circuit conductors of each trunk circuit in each line switch, a pair of the said wipers being used in extending a talking connection between a. calling line and a connected trunk circuit, a pair of the said wipers being used to extend a talking connection between a called line and a connected trunk circuit, at least one of the wipers of each set of wipers of a given line switch being solely used when the line is a. calling line, and an other of the wipers being solely used when the line is a called line, means to operate a calling line switch under substation control to make connection between a calling line and an idle trunk circuit, and means thereafter operative to cause the operation of a called line switch to make connection with the same trunk circuit.

4:. Ina telephone system, the combination with a plurality of telephone lines, substations for the lines, a main station, an individual line switch for each line at the main station, a plurality ottrunk circuits, terminals for the said trunk circuits connected to contacts of each of the said line switches, propelling means for each of the line switches, active switch wipers for each of the line switches, the said propellingmeans being adapted to move the said wipers successively over sets of contacts for each of the said trunk circuits, means to cause a calling line switch to make connection with the contacts associated with a non-engaged trunk circuit, and selecting apparatus associated with the selected trunk circuit to select the line switch of a called subscriber, and to cause the said line switch to be moved by its propelling means to cause its wipers to connect with the said connected trunk circuit.

5. In a telephone system. the combination with a calling subscribers line, an individual line switch therefor having wipers, means to cause the said line switch to select and to connect to a non-engaged one of a group of trunk circuits, said group of trunk circuits being common to a group of individual switches,-selecting apparatus thereafter operated through the said line switch and circuit conductors of the said selected trunk circuit under the control of calling subscriber substation apparatus to operate the line switch of a called subscribers line, means operated under the control of the said selecting apparatus to alter the electrical condition of one of the contacts of the connected trunk circuit, to cause the said called line individual switch to come to rest with. its wipers, engaging a set of contacts associated with the said connected trunk circuit, and means responsive to the connection between the said connected trunk circuit and the said called line switch wipers, to discharge the selecting apparatus from its association with the called line switch.

6. In a telephone system, the combination with a calling subscribers line, an individual line switch therefor having wipers, means to cause the said line switch to select and to connect to a non-engaged one of a group of trunk circuits, said group of trunk circuits being common to a group of individual switches, selecting apparatus thereafter operated'through the said line switch and circuit conductors of the said selected trunk circuit under the control of calling subscriber substation apparatus to operate the line switch of a called subscribers line, means operated under the control of the said selecting apparatus to alter the electrical condition of one of the contacts of the connected trunk circuit, to cause the said called line individual switch to come to rest with its wipers, engaging a set of contacts associated with the said connected trunk circuit, means responsive to the connection between the said connected trunk circuit and the said called line switch wipers, to discharge the selecting apparatus from its association with the called line switch, and means to restore the said selective apparatus to its normal position to make it available for the use of other calling subscribers.

7. In a telephone system, the combination with a calling telephone line, a called telephone line, a set of switch wipers including an outgoing switch wiper and sets of passive contacts for each of the lines, a stepping magnet adapted to propel the said switch wipers into successive contact with successive sets of passive switch contacts, trunk circuits including circuit conductors, circuit connections from each set of contacts to circuit conductors of a given trunk circuit, one at least of said circuit conductors being an outgoing conductor for use when connection is made to a trunk circuit by a calling line, and one other at least of said circuit conductors being an incoming circuit conductor for use when connection is made between the said trunk circuit and a called line, a switching relay for each of the switch wipers, a circuit conductor leading to a movable contact o1 the said switching relay and through a normal resting contact for the said movable contact to the said outgoing switch wiper, and through a normally disconnected ncense? .fior ct; or he idm e le n a o e trunks common to the lines,non-numerical:

' said incoming circuit conductor of such a trunk c rcu t as may be connected through the wipers of the; said .line sw tch.

I 8. Ina telephone system, thecombination with'a first line, a second line, a plurality of switchingmeans for each of thelines, a test circuit controlling each switching means, .a relay controlling each test c rcuit, and c1rcuit connections and apparatus to cause the said switching means to select and to connect with an idletrunkwhen the contacts of the a relay {are in one operative .condition,land to cause the said switch to select and connect to awparticular trunk when thesaid relay is in a-diiierent operative position.

' 9. aitelephone system, thecombination with a plurality oflines a plurality of link,

circuits, a switch for each line to connect it tofan idl e link circuit, and means ineluding, a relay for each switch to; cause thefsaid switch tio connectits associated line to aparticular link circuit.

i i a telephonesystem, the combination .with a. plurality of; lines, aplurality of link j circuits, a switch f or eachiline to connect V a Singleone of the said switcheshas alit. to idle link circuit, and means including a 'relay for each switch tocause the said switch to connect its associated line to aparticular link circuit to which ready been connected.

i .11. In a telephone system,thecombination V lines being a calling line, a plurality of with a pluralitybf; lines,,one of the said flink circuits, a switch'for each line to connectit to an idle link circuit, and means iny cluding a' relay tor-each switch to cause the said switch to connect itsassociated line to a particular link circuit to which a calling beetle 'ps mh s as already bee ,,COnnQc1-,ed a

with plurality of lines, substationsv for e naoi; or calling 1 ubs ation a paratus a linejs w itch because the said line switch to sociatedline to a part cular link circuit.

operate-under the control of the substation apparatus of another line to connect its as 1-751 t eilh ieeS stem;. fe n w th: plurality of linesim of h s '1 lines being acalling line, a pluralityof link circuits, a each line to connect it. to an idle link circuit, means including a i? eachswitch to mass ng said switch Y i connect its assets-tetanus aiparticular n t; raaa it'd-"which caning 31seer the led trunk circuit.

at se retes see y. a ee-.9? I e d and selective apparatus under the control of calling line apparatus to select and. operate the relay of a desired called line.

14. In a telephone system, the combination Iwith a plurality of lines, substations for the said lines, a plurality of link circuits common to the said lines, a single individual l ne switchfor each line, means to cause a line switch to operate underithe control of calling substation apparatus to connect its associated line wit-h an idle link circuit, means including a relay for each line switch to cause the said line switch to operate under the control of the substation apparatus of another line to connect its associated line to a particular link circuit, and Se lective apparatus under the control of calling line apparatus to select andoperate the relay of adesired called line. I

d 15. In a telephone system, the combination with a plurality of lines, one of the said lines. being a calling line, a plurality of link circuits, a switch for each line to connect it to an idle link circuit, a relay foreachj switch to cause thesaid switch toconnect its associated line to a particular link circuit to 'which a. calling line of thesaid switcheshas already been connected, selec tive apparatus under thecontrol of calling line apparatus to selectand operate the relay. of a desired called lin e,',and means responsive thereto. to cause its associated switch to. operate toconnect a calling line and called line toa previous calling-lineswitch-selected trunk circuit.

, 16. In a telephone system, the combination with a plurality of lines, substations for for the said lines, a plurality of link circuits common t-OgtlllC said. lines, a single individual line switch forlreach line, means to cause a line switchto operate under the control of calling'substatiOn apparatus to connect its associated line with an idle link circuit, a relayfor. each line switch to cause the said line switch to operate under the control of thesubstation apparatus of another line" to connect. its associated line to aparticular link circuit, selective apparatus under the control ofcalling line apparatus to select andoperate the relay of a desired called line, and means responsive thereto to cause its associated switch to operate to; connect a calling line. and j called line to a previous calling-line-switchsselecb 17.1In atelephone syste rn the combination dwith a plurality of" lines, a calling one of the said lines, a line switch for each line, a set of wipers for each-switch, comprising calling and called wipers, a plurality of trunk circuits, a set of contacts for each trunk circuit oneachswitch in the path of travel of the set ofwipers thereof, each set of trunk circuitcontacts comprising incomeseed Ou g i g er inal for esse ed net trunk circuit, calling line apparatus to control the operation of its switch to connect to an'idle trunk. circuit through calling s itch wipers and incoming trunk circuit contact terminals. and selective apparatus r said lines, a line switch for each line, a set of wipers for each switch, comprising calling and called wipers, a plurality of trunk circuits, a set of contacts for each trunk circuit on each switch in the path of travel out the set of] wipers thereof, each set of trunk circuit contacts comprising incoming and outgoing terminals for its associated trunk circuit, calling line apparatus to control the operation of its switch to connect to an idle trunk circuit through calling switch wipers and incoming trunk circuit contact terminals, selective apparatus operated under the control of the calling line apparatus .to cause a selected called line switch to connect to the calling line selected trunk circuit through .called wipers of the called line switch and outgoing terminal contacts of the said trunk circuit, and busy test means to prevent the operation of the said called line switch.

19. In a telephone system, the combination with a plurality of lines, a calling one of the said lines, a single individual line switch for each line, a set of wipers for each switch, comprisingcalling and called wipers, a plurality of trunk circuits, a set of contacts for I each trunk circuit on each switch in the path of travel of theset of wipers thereof, each set of trunk circuit contacts comprising incoming and outgoing terminals for its associated trunk circuit, calling line apparatus to control the operation of its. switch to connect to an idle trunk circuit through calling switch wipers and incoming trunk circuit contact terminals, and selective apparatus operated under. the control of the calling I line apparatus to cause a selected called line switch to connect to the calling line switch selected trunk circuit through called wipers of the called line switch and outgoing terminal contacts of the said trunk circuit.

20. Ina telephone system, the combination with a plurality of lines, a calling one of the said lines, a singleindividual line switch for each line, a set of wipers for each switch, comprising calling and called wipers, a plurality of trunk circuits, a set 01": contacts for each trunk circuit on each switch in the path of travel of the set of wipers thereof, each setof trunk circuit contacts comprising incoming and outgoing ten minals for its associated trunk circuit, calling line apparatus to control the operation of its switch to connect to an idle trunk circuit through calling switch wipers and in coming trunk circuit contact terminals, selec tive apparatus operated under the control, of the calling line apparatus to cause a select-ed called line switch to connect to the calling line selected trunk circuit through called wipers of the called line switch and outgoing terminal contacts of the said trunk circuit and busy test means to prevent the operation of the said called line switch.

21. In a telephone system, the combination with a plurality of lines, a calling one of the said lines, a line switch for each line, a set of wipers for each switch, comprising calling and called wipers, a plurality of trunk circuits, a set of contacts for each trunk circuit on each switch in the path of travel of the set of wipers thereof, each set of trunk circuit contacts comprising incoming and outgoing terminals for its associated trunk circuit, calling line. apparatus to control the operation of its switch to connect to an idle trunk circuit through calling switch wipers and incoming trunk circuit contact terminals, selective apparatus operated under the control of the calling line apparatus to cause a selected called line switch to connect to the calling line selected trunk circuit through called wipers of the called line switch and out-going terminal contacts of the said trunk circuit, busy test means to prevent the operation of the said called line switch, and an automatic ringing mechanism responsive to the selection of the called line switch to connect a ringing generator to the outgoing terminals of the said trunk circuit.

22. In a telephone system, the combination with a plurality of lines, substations for the said lines, a plurality of link circuits common to the said lines, a single individual line switch for each line, means to cause a line switch to operate under the control of calling substation apparatus to connect its asso-- ciated line with an idle link circuit, and means including a relay for each line switch to cause the said line switch to operate under the control of the substation apparatus of another line to connect its associated line to a particular link circuit to which a single one of the said switches has already been con nected.

23. In a telephone system, the combination with a plurality of lines, substations tor the said lines, a plurality of-link circuits common to the said lines, a single individual line switch "for each line, means to cause a line switch to operate under the control of calling substation apparatus to connect its associated line with an idle link circuit, means including a relay for each line switch to cause the saidline switch to operate under the control of the substation apparatus oi [calling-line is connected to select the relay of 'adesjired called lineswitch. v

7 tion with a plurality of lines, a calling one I {jswitchf o'r eachlin'e,a set of wipers for each emes 241 'In, a" telephone system, the combina- Iof thesaid' lines, a single individual line (switch, rising calling and called wipf erjs, a plurality of trunk circuits, a set of fcontacts foreachtrunk circuit in'each switch ;the,pathfof travelofthe set of wipers. 'th' f each setfof trunkfcircuit contacts [incoming and outgoing termiit's switch to connect toQan' idle -trunfik circuit ,threugh calling switch wiper'sfand -incom-,

fling tifun circuit contact terminals, selective apparatus operated under the control of the calling line apparatus to cause a selected ca'lld li'ne switch to connect to the calling line selected trunk circuit through called wipers of the called line switch and outgoing terminal contacts of the said trunk circuit, busy test means to prevent the operation of the said called line switch, and automatic ringing mechanism responsive to the selection of the called line switch to connect a ringing generator to outgoing terminals of the said trunk circuit. 25. In a telephone system, the combination with a plurality of lines, a calling one ofthe said lines,'a line switch for each line, a set of wipers for each switch, comprising calling and called wipers, a plurality of trunk circuits, a set of contacts for each trunk circuit on each switch in the path of travel of the set of wipers thereof, each set of trunk circuit contacts comprising incoming and outgoing terminals of the associated trunk circuit, calling line apparatus to control the operation of its switch to connect to an idle trunk circuit through calling switch wipers and incoming trunk circuit contact terminals, selective apparatusoperated under the control of the calling line apparatus to cause a selected called line switch to connect to the calling line selected trunk circuit through called wipers of the called line switch and outgoing terminal contacts of the said trunk circuit, busy test means to prevent the operation of the said called line switch, an automatic ringing mechanism responsive to the selection of the called line switch to connect a ringing generator to the outgoing terminals of the said trunk circuit, and means to disable the said ringing generator connection under the control ofcalled line apparatus. I

26. In a telephone system, the combination with a plurality of lines, a calling one ssociated. trunkcircuit,@calling lliie'l appai ,tus, tocontrol,the operation of of the said lines, a line switch foreaclrli ie, a set of wipers for each switch, compris ng calling and called wipers, afplurality' of trunk circuits, a set of contacts for, each trunkcircuit on each Switch in the path of travel of the set of wipers thereof, each set of trunk circuit contacts comprising incoming and outgoing terminals for its associated trunk circu t, calling line 'ap paratus to control the operation of its sw tch to con switch wipers and incoming trunk circuit contact terminals, selective ap'paratusoperatedlunder'the control'gof the calling line,ap-' paratus to cause aselected calledline switch to connect to the calling line selected trunk circuit through called wipers of the call'ed line switch and outgoing terminal contacts [of the said trunk circuit, busy test means to prevent the operation of the" said called line sw tch, an automat c ringing mechaIil'Sm re- "sponsive to the selection of the called line switch to connect at ringinggeneratorlto the outgoing terminals of the said trunk cir- 'cuit, substation for each of the lines," and means responsive to the connection of the substation of the called line to its line conductors to disable the said ringing generator connecting circuit.

27. In atelephone system, a calling line, a called line, a line switch for the individual use of each line, each'line switchbeing provided with contacts and wipers normally engaging certain of said contacts, link circuits terminating in said contacts, means for operating the individual switch of a calling line to seize a link circuit, means controlle over the calling line for causing the individual line switch of the called line to seize the link circuit with which the calling line switch is in engagement. 7

28.; Ina telephone system, a calling line, a

called line, a line switch for the individual use of each line, each line switch being provided with contacts and wipers arranged to remain in engagement with thecontacts last used, link circuits terminating in said contacts, means for operating the individual switch of a calling line to seize a link circuit, means controlled over the calling line for causing the individual line switch of the v a nect to an'idle trunk circuitthrough calling called line to seize the link circuit with which link circuit, means controlled over the calling line for causing the individual line switch of the called line to seize the linkcircuit with which the calling line switch is in engagement. y

30. In a telephone system, a group of telephone lines, a switch for each line having wipers, v link circuits accessible to said switches, means for causing the line witches of a calling line and a called line to seize'opv group.

31, In a telephone system, agronp'ot telephone lines, Ilink circuits, a switch having contacts and wlpers ind vidual to each line,

each switch being arranged to hold its wipers in engagement with the contacts last used, means for causing the line swltches of a calling and a called'line to seizeopposite ends of a link circuit in completing a conversational circuit, and means, for completing one connection at a time in said groups 32. In 'atelephone system, an individual line switch for each line having contacts,

trunk conductors terminating ateach end in contacts of said line switches, said conductors being continuous between said contacts, a source of transmitter current bridged across said trunks, andmeans for causing the call; ing and called line switchesto seize a trunk in completing" a telephone connection.

33. In a telephone system, a group of telephone lines, a plurality of rotary step by step non-numerical v switches, each switch having contacts and wipers certain of which are individual to'each telephone line, each switch being arranged to hold its wipers in the position last used, a plurality of link circuits. means for causing the switch wipers of a calling and a ,called telephone line to set up and hold a telephone connection through a linkcircuit and means for completing the setting of one connection at a time in said group. i 4

In witness whereof, I hereunto subscribe my name this 2nd day of January, A. D. 1919. v e e FRANK M. SLOUGH. 

